1. Field of the Invention
The field of this invention is four stroke cycle, spark ignition, gasoline engines, and, more specifically, the valve driving mechanism and torque control means for such engines.
The term "conventional, four stroke cycle, gasoline engine" is used hereinafter and in the claims to mean the known and conventional combinations of cylinders, cylinder heads, pistons operative within said cylinders and connected to a crankshaft via connecting rods, engine oil supply system, cooling system, spark ignition system, flywheels, starting system, fuel supply system, fuel-air mixing system, exhaust pipes, intake pipes fitted with the usual torque controlling throttle plate, intake valve and intake valve drive mechanism, exhaust valve and exhaust valve drive mechanism, etc., as necessary for the proper operation of said conventional, four stroke cycle gasoline engine. The term "conventional intake valve and exhaust valve driving mechanism" is used hereinafter and in the claims to mean the known and conventional combinations of cams driven at half crankshaft speed to actuate valve lifters and push rods which in turn actuate rocker arms acting directly on the engine intake and exhaust valves to open these valves and return springs acting directly on the engine intake and exhaust valves to close these valves, as used commonly on conventional, four stroke cycle, gasoline engines. The term conventional intake valve and exhaust valve driving mechanism is used hereinafter and in the claims to include also the known and conventional combinations of overhead cams driven at half crankshaft speed to actuate valve lifters acting directly on the engine intake and exhaust valves to open these valves and return springs acting directly on the engine intake and exhaust valves to close these valves, as used occassionally on conventional, four stroke cycle, gasoline engines. The term "usual torque controlling throttle plate" is used hereinafter and in the claims to refer to the throttling valve interposed between the fuel-air mixing device and the intake air pipe connecting to the inlet port of the engine intake valve, said throttling valve acting to control engine torque by throttling the air-fuel mixture on its way into the engine cylinder during the intake stroke and thus reduce the pressure and quantity of the mixture in the cylinder, as used commonly to control torque of conventional, four stroke cycle, gasoline engines.
2. Description of the Prior Art
When the speed of a conventional four stroke cycle gasoline engine, equipped with the conventional intake valve and exhaust valve driving mechanism is increased in order to increase the power output of the engine a speed is finally reached beyond which the engine fails to function properly due to the occurrence of "valve float." Engine valves are said to "float" when the force of the valve closing, return springs is inadequate to overcome the inertia of the mass of the valve, rocker arm, push rod and tappet mechanism and in consequence this mechanism does not follow the cam during the closing of the valve. When the engine designer seeks to prevent valve float by increasing the strength and force of the return spring his efforts are partially offset by the necessarily increased mass and inertia of the return spring itself. Higher engine speeds without valve float can indeed be obtained by using overhead cam shafts which allow reducing the mass whose inertia must be overcome by the return spring. But overhead camshafts are expensive and still have a definite upper limit of engine speed beyond which valve float occurs.
The temperature of the exhaust valves of a conventional four stroke cycle gasoline engine increase rapidly as engine speed is increased due to increased net flow rate of hot exhaust gas over the valve. As a result the exhaust valve deteriorates more rapidly and has a shorter useful life at increased engine speeds.
Some of those problems of the automobile engine created by the shortage of fuel on the one hand and the public desire for reduced exhaust emissions on the other hand can be alleviated if the gasoline engine can be modified to operate properly over a very wide range of speeds. In this way an engine of small displacement can be operated at lower speeds with high efficiency, low fuel consumption, and reduced emissions to propel the vehicle at moderate speed and grade conditions. This same small displacement engine can be operated at higher speeds with high power output to propel the vehicle on steep grades or at high speeds or for rapid acceleration. Since the majority of the running of an automobile engine is at moderate speeds on moderate grades at net improvement in both fuel consumption and exhaust emissions can be realized by substituting the above described small displacement, wide speed range gasoline engine for the present large displacement, moderate speed range gasoline engine required to give the same acceleration, top speed and hill climbing capability. To achieve this desireable, small displacement, wide speed range gasoline engine design will require extensive changes to many portions of the engine, the vehicle transmission and the vehicle drive line but this invention concerns only modifications to the intake valve and exhaust valve driving mechanism so that it will operate properly over a very wide range of engine speeds.
The conventional four stroke cycle gasoline engine operates on the approximate equivalent of the Otto cycle and, in consequence, the temperatures at any point in the engine process do not change appreciably when engine torque is reduced by operating the usual torque controlling throttle plate to throttle the intake air-fuel mixture. Throttling acts to reduce the pressure and density of the intake mixture in the cylinder and in this way the quantity of mixture in the cylinder is reduced and hence the torque is reduced. The temperatures of the air-fuel mixture in the cylinder and of the burned gases after combustion are not, however, appreciably changed by throttling. The concentrations of the undesirable oxides of nitrogen formed during combustion decrease as the temperatures in the cycle are decreased, particularly the maximum temperatures in the cycle following completion of combustion. Hence the oxides of nitrogen concentration in the exhaust gas of a conventional four stroke cycle gasoline engine equipped with the usual torque controlling throttle plate do not change appreciably as engine torque is reduced as is shown in references A and B. This is a serious disadvantage of the conventional four stroke cycle gasoline engine in automobile and other applications where most of the engine operation is at reduced torque settings.
The usual torque controlling throttle plate maldistributes the unevaporated liquid portions of gasoline between the several cylinders of a multicylinder gasoline engine. In consequence some cylinders operate too rich in fuel for the amount of air available and increased quantities of unburned hydrocarbon and carbon monoxide are emitted via the exhaust gas of these cylinders.
Emissions of oxides of nitrogen, unburned hydrocarbons and carbon monoxide by gasoline engines are widely recognized as undesireable since they are pollutants themselves and some of them participate actively in the creation of other types of harmful air pollutants. It is the reduction of these harmful exhaust emissions which constitutes an important beneficial object of my invention.
The usual torque controlling throttle plate produces, at reduced torque, an intake manifold pressure necessarily reduced well below the exhaust manifold pressure and the efficiency of the engine is reduced by the loss due to pumping the gas against this difference in manifold pressure.